The present invention relates to a hologram recording/reproducing device and an optical unit.
The development of a hologram recording device for recording data using holography is being pursued.
In the hologram recording device, modulated signal light (that is, signal light upon which data is superposed) and reference light which is not modulated are generated from laser light and irradiate the same location of a hologram recording medium. This results in interference between the signal light and the reference light at the hologram recording medium, causing a diffraction grating (that is, a hologram) to be formed at an irradiation point. As a result, the data is recorded on the hologram recording medium.
Irradiating with the reference light the hologram recording medium on which the data has been recorded causes diffraction light (reproduction light) to be generated from the diffraction grating formed during the recording. Since the reproduction light includes the data superposed upon the signal light during the recording, the recorded signal can be reproduced by receiving the reproduction light by a light receiving element.
In order to record a large amount of information on the hologram recording medium, a large number of holograms may be formed on the hologram recording medium. In this case, holograms are not necessarily formed on different locations of the hologram recording medium. Accordingly, what is called multiple recording for forming a plurality of holograms on the same location (that is, an area where the holograms are superposed upon each other) of the hologram recording medium may be performed.
The development of a hologram recording device whose storage capacity is increased by phase correlation multiplexing, which is one type of multiple recording, is being pursued (refer to, for example, Japanese Unexamined Patent Application Publication No. 11-242424).
In the aforementioned document, phase correlation multiplexing is achieved by using a phase mask for reference light. A phase mask may also be used for signal light to suppress a dc component of a hologram signal to be recorded.
However, when phase masks are to be used for both the signal light and the reference light, not only is it typical to use a phase mask for the signal light and a phase mask for the reference light, but also parts for these phase masks are typically used, thereby resulting in the problem that an optical system becomes sophisticated.
When these phase masks are used, noise tends to be produced. Here, when a filter for removing the noise is used, the amount of light with which the hologram recording medium is irradiated is reduced.
Accordingly, it is desirable to provide a hologram recording/reproducing device and an optical unit, whose optical system can be simplified and which can restrict generation of noise and a reduction in the amount of light even if a phase modulating element is used for both signal light and reference light.